Single-Joint Angle Computation using Inertial Sensors with Feedback on Smartphone

Human joint kinematics is an important biomarker of the joint and muscles' strength responsible for its actuation. Restriction to joint movement directly affects the limb's interaction with its environment and puts other joints at risk of developing compensatory motions. In this study, a portable and wearable sensor device is developed that measures the elbow joint angle in real-time and provides its feedback on a smartphone application to the user. The sensor system is equipped with two inertial measurement units - one at each upper arm and forearm. The algorithm computes the joint angle from the orientation of the forearm segment relative to the upper arm using quaternions from each respective inertial sensor. The measured joint angle is validated against the gold standard Vicon Motion Capture system. A couple of day-to-day activities are performed where the device's applicability is shown in measuring the joint's range of motions. Users and clinicians can utilize such portable sensor devices with quantitative biofeedback features for joint rehabilitation, training, and range of motion while performing joint-specific movements in sports activities or other common tasks. The study, also, provides a platform to develop single-joint angle computation wearable devices that can measure joint kinematics outside the stationary laboratory facilities in daily life conditions.